Belemnites were squid-like carnivores with a soft body around an internal, pencil-shaped shell. Early forms evolved in the Carboniferous period and are thought to have evolved from the same ancestors as the ammonites. Belemnites were common from the Lower Jurassic period to the end of the Cretaceous period and became extinct at the same time as the dinosaurs - approximately 65 million years ago.

The cuttlefish is the modern-day relative of the belemnite. Belemnites were efficient carnivores that caught small fish and marine animals with their tentacles, and ate them with their beak-like jaws. Their tentacles were different to the modern squid, as they had hooks instead of suckers to grab prey. They were built for speed and probably lived in shoals and fossil evidence shows they formed a major part of the diet of ichthyosaurs.